1. Field of the Invention
The present invention relates to a battery charging apparatus for charging a secondary battery, such as a nickel•cadmium battery (Ni—Cd battery), a nickel•hydrogen battery or the like, and more particularly, to a battery charging apparatus capable of being used under the power condition in which the variation of the input voltage applied to the battery charging apparatus is severe.
2. Description of the Related Art
A secondary battery with a high capacity, such as the Ni—Cd battery or the nickel•hydrogen battery or the like, is widely used as a power source for a portable device, such as an electrical tool. Meanwhile, as a capacity of the secondary battery increases, the charging device for charging the battery in a short time has been developed to have a large output and a high capacity.
The following charging device has been developed. When the charge is performed by the charging device, the charging device detects various information of the battery, such as a battery voltage during the charge, a battery temperature, and a charging current, to prevent the life span of the battery from being reduced by the charge with a large current, and then performs an optimum charge control on the basis of the detected information on the battery. For example, the charging device, which detects the battery voltage during the charge to control the charging current, is disclosed in U.S. Pat. No. 5,973,480.